Some companies, like Speck, have said that their iPhone 6 cases will fit the new iPhones. Check the website of your case manufacturer and see if they’ve made a statement about their cases.

You really need to look at the new iPhones in person to make sure your old case fits. But by the looks of the product photos, the cameras and side buttons haven’t moved, so your case alignment should be fine. The dimensions of the new iPhones have changed, however, which will determine if you can still use your case.

iPhone 6s

The iPhone 6s is almost the same size as the iPhone 6—in inches it's the same height and width, but the 6s is bigger by fractions of a millimeter. The iPhone 6s is deeper, measuring 0.28 inches (7.1 millimeters). That’s 0.01 inches (0.2 mm) thicker than the iPhone 6. And the 6s weighs more, too.

There’s a good chance your iPhone 6 case can fit on the iPhone 6s. If you’re using a silicon or leather case, your case probably has stretched a little with age, so it may fit fine on a new iPhone 6s. Hard-shell cases are a different story—they’ll probably fit, unless the fit is already very tight on your iPhone 6.

iPhone 6s Plus

The iPhone 6s Plus is bigger overall than the iPhone 6 Plus. It’s taller, wider, deeper, and even weighs more than its predecessor—we’re talking .1 or .2 mm on each dimension, so it’s not obviously bigger, which means you might think that your case will fit.

And it may, if you have a silicon or leather case that’s developed some give over time. It’s possible, though, that an iPhone 6 Plus hard-shell case that needs a snug fit won’t really fit on the iPhone 6s Plus.